Compound curved spring motor



Jan; 16, 1968 E, E, os'f R I I 3,363,891

comPounn CURVED SPRING MOTOR Filed April 11, 1966 INVENTORV Eowm' E. Fos'rER I ATTORNEY United States Patent 3,363,891 CGMJPOUND CURVEI) SPRING MOTOR Edwin E. Foster, 1801 Camp Craft Road, Austin, Tex. 78746 Filed Apr. 11, 1966, Ser. No. 541,787 Claims. (Cl. 267-1) This invention relates in general to springs, and, more particularly, to a spiral spring of enhanced motive power characteristics.

It is an object of the present invention to provide a spring motor of the spiral type having applied stresses for rendering said spring of equal power to springs of greater size and thickness.

It is another object of the present invention to provide a spring motor of the spiral type wherein the unwinding force is a composite of both longitudinal and cross curve components, so as to produce considerably greater power than heretofore attained by springs of like weight and dimensions.

It is a further object of the present invention to provide a spring motor of the spiral type being so uniquely prestressed both longitudinally and transversely that when unrestrained for wound condition, the entire length of the ribbon becomes effective to expend its force in substantially a constant manner.

It is a still further object of the present invention to provide a spring motor of the spiral type having a novel applied cross-curvature, whereby, when the spring moves between Wound and unwound condition, while restrained as within a casing, a storing and releasing of energy is brought about for supplementing the applied longitudinal force.

It is another object of the present invention to provide a spring motor of the spiral type which is simple in construction; which may be economically produced; which is extremely durable and reliable in usage, having more fatigue life than current springs of like size and weight, which has myriad usages and applications; and which may be formed from ribbon pre-treated by known techniques.

Other objects and details of the invention will be apparent from the following description, when read in connection with the accompanying drawing (one sheet) wherein- FIGURE 1 is a side elevational view of a spiral spring constructed in accordance with and embodying the present invention showing a portion of the ribbon in uncoiled, extended condition.

FIGURE 2 is a transverse sectional view taken on the line 2-2 of FIGURE 1.

FIGURE 3 is a transverse sectional view taken on the line 33 of FIGURE 1.

, FIGURE 4 is a side elevational view of the spring of the present invention in wound condition.

FIGURE 5 is a transverse sectional view taken on the line 55 of FIGURE 4.

FIGURE 6 is a side elevational view of the spiral spring of the present invention in unwound condition.

FIGURE 7 is a transverse sectional View taken on the line 7-7 of FIGURE 6.

Referring now particularly to FIGURES 1 and 2, A generally designates a coil spring constructed from flat ribbon made from any one of suitable materials, such as spring steel, brass, and the like. The flat ribbon of spring A is subjected to tensioning devices, such as disclosed in my United States Patent No. 2,609,101, issued Sept. 2, 1952, to produce desired residual stresses to cause spring A to form a spiral coil composed of a plurality of tightly Wound convolutions. Thus, spring A is so prestressed as to bias same into a tightly coiled condition of repose. An extended length of spring A, as indicated generally at 1, would assume a concave-convex cross-section,

in which the concave side would be toward the center of the coil. This concave-convex cross-section is believed to be due to the stresses Within the spring A when unwound and hence will be referred to herein as the natural crosssection in that such occurs notwithstanding the fact that the coil spring is constructed from a ribbon having a substantially flat cross-section.

The ribbon of spring A is also subjected to a bending operation, die-forming, or the like, to produce a concaveconvex cross-section, designated 1 (FIGURE 2.) which is additive to, or supplementary of, the aforesaid natural cross-curvature. Wherefore, the concave side will, in an extended length of the spring, be directed toward the cen' ter of the coil, but will be formed on a lesser radius than the aforesaid natural cross-curvature. Such formed, en hanced, cross-section may be imparted to the ribbon either prior to the coiling operation, concurrently therewith, or subsequent thereto. Tooling having co-operating rollers with complementary peripheral contouring may be utilized for imparting the additional cross-curvature to the ribbon.

In addition to providing spring A with an increased cross-curvature, the particular forming operation is also adapted to cover a stretching of the edges or marginal portions of spring A, as at 2, 2, which edges are thus stretched greater than the center portion. As a result of the edge-stretching operation, spring A, when in repose or coiled condition, will assume the shape shown in FIG- URE 3, wherein the convex side is directed toward the center of the coil. With spring A in unwound state, the stretched edges 2, 2, will be normally in tension, with the interventing portion in compression. It will thus be up preciated that with the edges of the said ribbon being stretched beyond their elastic limit, the resultant crosscurvature bias of spring A is such that the same will move from a condition wherein the convex side will be directed toward the center of the coil (FIGURE 3) to a condition wherein the concave side will be directed toward the cen ter of the coil (FIGURE 1) when spring A moves from wound to unwound condition.

In addition to the formed cross-curvature above described, spring A is subjected to a back-winding operation wherein the outer end of the coil, as at 3, may be secured to an arbor, and then back-wound thereon so that when a length of ribbon is extended from the coil,

the same will assume the back bent curved line as shown at 4 in FIGURE 1.

In View of such applied stresses, in order for an extended portion of spring A to return to coiled condition, force is necessary to effect such result because the crosssectional curve must be caused to move from a concave shape to a convex shape, which change presents a predetermined force opposed by the longitudinal force of spring A, so that depending upon which is the greater of such contending forces, the extended portion of spring A will either naturally return to coiled condition, by a relatively greater longitudinal force, or will necessarily be urged into such condition of repose by extrinsically applied force.

Although it has been known that the cross-curve developed in a flat ribbon spring when moving from wound condition to extended condition tends to make the extended portion of the spring stiffen and hence stronger; heretofore, efforts to utilize such transverse curvature for increasing spring motor power when the same is moving between wound and unwound condition have proved fruitless. Current spiral coil springs formed from ribbon stock have relied upon the longitudinal force for spring power. The problem has thus been the failure to develop a cross curvature which renders the spring capable of giving and taking energy when changing from Wound to unwo und condition, and the reverse thereof. Accordingly, in known spring constructions, the same have moved between concave-convex cross-curvature when in straight line condition to transversely flattened or straight cross-sectional condition, when wound, in which latter condition, the spring is substantially devoid of a force component from such flattened state.

In the present invention, spring A is so formed and stressed that substantial force is provided the spring by reason of the novel cross-curvature, together with the compound curved character of the spring, which is capable of giving and taking energy when moving between such conditions.

Referring now to FIGURE 4, the extended portion 1 of spring A, as shown in FIGURE 1, is secured as by rivet or the like 1!) to the hub 11 of a motor casing 12. The hub 11 is revolved in the direction shown by the arrow, for backwinding spring A thereon. The now outer or opposite end of said spring A is fixedly engaged to the inner face of wall 13 of casing 12. As indicated in FIG- URE S, the cross section of spring A as thus wound about hub 11 is nearly, but definitely not quite, flat, as at 14, there being, however, a very definite vestige of cross curvature. It will be appreciated that in such condition, as shown in FIGURE 5, the longitudinal curve of spring A has gone from the coiled condition of repose shown in FIGURE 1 to the extreme back-bent condition. As spring A unwinds from the condition shown in FIGURE 4, as upon clockwise rotation of hub 11, the coil will finally spirally come to rest against the inside peripheral wall 13 of casing 12 (FIGURE 6). In travelling between the positions shown in FIGURES 4 and 6, the cross curve of spring A gradually changes from the nearly fiat condition 14 (FIGURE 4) to an increased cross-curved condition indicated at 15 in FIGURE 7, induced by the above-described marginal stretching and added cross curvature.

As spring A moves from a fully backwound condition upon hub 11 (FIGURE 4) to restrained condition against the wall of casing 12, the same is endowed with enhanced power by reason of the substantial stiffening brought about by the development of the relatively deep concave-convex cross-curve 15. As spring A is returned to wound condition upon hub 11, a substantial storing or taking of energy is developed through the depressing of the cross-curvature from the condition shown in FIGURE 7 to that shown in FIGURE 5. Accordingly, upon subsequent unwinding of spring A from hub 11, the same will give energy as its cross-section assumes the condition shown in FIGURE 7. The marginally stretched portions of spring A which are normally under tension, materially conduces to the capability of spring A in giving and taking such energy, so that the power of spring A is not determined solely by longitudinal force, but by such force together with the transverse forces, which have hitherto not been deemed obtainable.

The motor shown in FIGURES 4 through 7, inclusive, does not at any time return to the coiled condition of repose, but merely moves between fully backwound condition and that shown in FIGURE 6. Casing 12 restricts movement of spring A to the extent requisite to allow the cross curvature to make the change of shape necessary for the storing and releasing of energy for supplementing the force of the longitudinal curve.

By the present invention, maximum usage is made of both the cross-curve and the longitudinal curve so that spring A is provided with a motive power considerably greater than that of springs of like size, weight, and thickness. By reason of the uniquely applied stresses, springs of the present invention have myriad usages, such as in all types of devices utilizing spiral spring motors, for instance, cameras, clocks, toys, measuring tape reels, etc., and are of such strength as to be suitable for cantilever usage.

In addition to springs pre-tensioned as in the manner set forth in United States Patent 2,609,191, the provision of the compound curve to springs formed from flat steel ribbon and pre-treated in other tensioning manners has also conclusively proved to endow same with substantially increased power characteristics, so that the provision of the combination of the developed cross-curvature, the marginal stretching, and the subjection of such straight curved stress into the compound curved stress by backwinding produces force properties believed to the present time to be beyond the capability of springs of this type.

It should be understood that changes and modifications in the formation, construction, arrangement, and combination of the several parts of the compound curved spring motor may be made and substituted for these herein shown and described without departing from the nature and principle of my invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. A spring comprising a ribbon having a longitudinally stressed force urging said spring into a coil of wound convolutions when in repose, said longitudinal stress tending to cause a natural concave-convex cross-section in said spring when extended from its wound condition, said spring further having a formed cross-curvature which is in the same direction as, and supplementary of, said natural concave-convex cross-section, and said spring also having edge portions stretched beyond their elastic limit for causing the concave side of said spring cross-curvature to assume opposed relationship, with respect to the center of said coil when the spring is in extended condition and in coiled condition.

2. A spring as defined in claim 1, and further characterized by the concave side of said cross-curvature being directed toward the center of the coil when said spring is extended, and being directed away from said coil when said spring is in coiled condition.

3. A spring as defined in claim 1, and further characterized by said spring being further longitudinally stressed in a direction opposite to that urging said spring into a coiled condition of repose.

4. A spring as defined in claim 1, and further characterized by the spring being longitudinally back-bent so that when extended, it will assume a longitudinally curved condition which is directed away from the curve of the coil.

5. A spring as defined in claim 4, and further characterized by a pair of concentric, relatively rotatable drums for the coil of spring ribbon, the normally outer end of the ribbon being secured to the outer surface of the inner of said drums, and the normally inner end of the ribbon being secured to the internal surface of said outer drum for movement between backwound condition on said inner drum and disposition against the said internal surface of said outer drum in which latter state said spring will assume a cross-curved condition.

References Cited UNITED STATES PATENTS 2,833,534 5/1958 Foster 267-1 2,956,795 10/1960 Foster 2671 EDGAR W. GEOGHEGAN, Primary Examiner. 

1. A SPRING COMPRISING A RIBBON HAVING A LONGITUDINALLY STRESSED FORCE URGING SAID SPRING INTO A COIL OF WOUND CONVOLUTIONS WHEN IN REPOSE, SAID LONGITUDINAL STRESS TENDING TO CAUSE A NATURAL CONCAVE-CONVEX CROSS-SECTION IN SAID SPRING WHEN EXTENDED FROM ITS WOUND CONDITION, SAID SPRING FURTHER HAVING A FORMED CROSS-CURVATURE WHICH IS IN THE SAME DIRECTION AS, AND SUPPLEMENTARY OF, SAID NATURAL CONCAVE-CONVEX CROSS-SECTION, AND SAID SPRING ALSO HAVING EDGE PORTIONS STRETCHED BEYOND THEIR ELASTIC LIMIT FOR CAUSING THE CONCAVE SIDE OF SAID SPRING CROSS-CURVATURE TO ASSUME OPPOSED RELATIONSHIP, WITH RESPECT TO THE CENTER OF SAID COIL WHEN THE SPRING IS IN EXTENDED CONDITION AND IN COILED CONDITION. 